Allow pgpool_setup to test sample scripts and sample config files contained in RPMs.

Allow pgpool_setup to test sample scripts and sample config files contained in RPMs.

Currently, pgpool_setup generates scripts (e.g. failover.sh, follow_primary.sh) to test pgpool.

This commit addes a new option "-c" in src/test/regression/regress.sh
and a new environment variables TEST_SAMPLES in pgpool_setup.
Option "-c" enables TEST_SAMPLES and allows pgpool_setup to test sample scripts and
sample config files contained in RPMs.

This commit also changes "backend_hostnameX = '/tmp'" to "backend_hostnameX = 'localhost'".