Fixes #39 - NullPointerException when running "mvn liquibase:diff"

The `Table` instance obviously doesn't have a primary key set yet, since that is what we are trying to do, so set the primary key name from the `hibernatePrimaryKey` instead.
Merge pull request #40 from vetler/patch-1

Fixes #39 - NullPointerException when running "mvn liquibase:diff"
Merge branch 'master' of https://github.com/ssiahetiong/liquibase-hibernate into ssiahetiong-master

Conflicts:
	src/main/java/liquibase/ext/hibernate/snapshot/TableSnapshotGenerator.java
Use defaultSchemaName as the connection schema