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## Environment
**Liquibase Version**: 4.2.2

**Liquibase Integration & Version**: Maven

**Liquibase Extension(s) & Version**: NA

**Database Vendor & Version**: com.ibm.db2:db2jcc_license_cisuz & 9.7.5

**Operating System Type & Version**: Windows 7 Enterprise

## Description
I tried to implement Liquibase for my IBM DB2 zos database and when i run liquibase:generateChangeLog command, I’m getting the following error.

Error setting up or running Liquibase: liquibase.command.CommandExcecutionExceptoin: liquibase.exception.DatabaseException: Error executing SQL select CONSTRAINT_NAME, COLUMN_LIST as COLUMN_NAME, constraint_schema as CONSTRAINT_CONTAINER from information_schema.constraints where constraint_type=‘UNIQUE’ and …; DB2 SQL Error: SQLCODE=-204, SQLSTATE=42704, SQLERRMC=INFORMATION_SCHEMA.CONSTRAINTS, DRIVER=4.25.13

SQLCODE=-204, object not found, Basically the table/schema is not found.

When I ran the same command in debug mode, I could see that in the following class, liquibase/UniqueConstraintSnapshotGenerator.java at master · liquibase/liquibase · GitHub there is no logic to handle DB2z and hence it is considering no specific handler for RDBMS was provided and assuming INFORMATION_SCHEMA.

We do have logic for DB2Database, but not DB2ZDatabase .

## Steps To Reproduce
1. Create a maven project
1. Add the following dependencies in pom.xml
  * com.jbm.db2:db2jcc4 & 4.25.13
  * com.ibm.db2:db2jcc_license_cisuz & 9.7.5
1. Add the following plugin to pom.xml
  * org.liquibase:liquibase-maven-plugin & 4.2.2
  * in the <configuration> tag, add <propertyFile> and specify the property file liquibase-dev.properties to run
1. In the property file liquibase-dev.properties, I specified the follwoing
  * url(jdbc:db2://<hostname>:<port>/currentSchema=<schemaName>;) , username, password, ouputChangeLogFile, driver(com.ibm.db2.jcc.DB2Driver).
1. Run mvn clean and run mvn liquibase:generateChangeLog

## Actual Behavior
When I run mvn liquibase:genereateChangeLog, I'm getting the below error,

Error setting up or running Liquibase: liquibase.command.CommandExcecutionExceptoin: liquibase.exception.DatabaseException: Error executing SQL select CONSTRAINT_NAME, COLUMN_LIST as COLUMN_NAME, constraint_schema as CONSTRAINT_CONTAINER from information_schema.constraints where constraint_type=‘UNIQUE’ and …; DB2 SQL Error: SQLCODE=-204, SQLSTATE=42704, SQLERRMC=INFORMATION_SCHEMA.CONSTRAINTS, DRIVER=4.25.13

## Expected/Desired Behavior
mvn liquibase:generateChangeLog should generate the change log for IBM DB2z based on the current specified database schema.

## Screenshots (if appropriate)
If applicable, add screenshots to help explain your problem.

## Additional Context
Add any other context about the problem here.


/**
     * To support bulk query, the resultSet must include a CONSTRAINT_CONTAINER column for caching purposes
     */
    protected boolean supportsBulkQuery(Database database) {
        return !(database instanceof DerbyDatabase)
                && !(database instanceof FirebirdDatabase)
                && !(database instanceof SybaseASADatabase)
                && !(database instanceof Ingres9Database)
                && !(database instanceof InformixDatabase);
    }
    /**
     * Gets an SQL query that returns the constraint names and columns for all UNIQUE constraints.
     *
     * @param database A database object of the InformixDatabase type
     * @param schema   Name of the schema to examine (or null for all)
     * @param name     Name of the constraint to examine (or null for all)
     * @return A lengthy SQL statement that fetches the constraint names and columns
     */
    private String getUniqueConstraintsSqlInformix(InformixDatabase database, Schema schema, String name) {
        StringBuilder sqlBuf = new StringBuilder();
        sqlBuf.append("SELECT * FROM (\n");
        
        
        for (int i = 1; i <= 16; i++) {
            if (i > 1)
                sqlBuf.append("UNION ALL\n");
            sqlBuf.append(
                    String.format("  SELECT\n" +
                                    "    CONS.owner,\n" +
                                    "    CONS.constrname AS constraint_name,\n" +