Add ability to override JSR-352 baseContext.xml

While existing functionality provided the ability to override the
components provided in the baseContext.xml (as required for JSR-352
functionality) at a job by job level, this commit allows a user to
specify a base context for all of the JSR-352 based jobs within a JVM.
To set the location of the custom base context, a JVM property
JSR-352-BASE-CONTEXT should be set.

BATCH-2290
Make use of current working dir explicit for compatibility with H2 1.4

H2 1.4 requires that file paths that are relative to the current
working directory declare this explicitly, i.e. the path
file:/some-dir must now be file:./some-dir.

This commit updates DatabaseTypeIntegrationTests to meet the
above-described requirement, thereby allowing the tests to pass when
run against H2 1.4.x.