LU-1538 tests: standardize test script init dne-part-1

Standardize the initial Lustre test script initialization for
clarity and consistency.

The LUSTRE path is already normalized in init_test_env(), so this
doesn't need to be done in the caller.  Use $(...) subshells instead
of `...` in the affected lines.  Remove NAME, SRCDIR, PATH, MULTIOP,
SETUP, CLEANUP, CHECKSTAT, TMP, SAVE_PWD, variable initialization,
since it is already done in init_test_env() or not needed in the test
scripts.  Remove all calls to get_lustre_env() in the test scripts
since this is called in init_test_env().

Move all definitions of ALWAYS_EXCEPT and SLOW to after
init_test_env() and init_logging() and call build_test_filter()
immediately after the ALWAYS_EXCEPT and SLOW definitions.

Test-Parameters: trivial
Test-Parameters: testgroup=review-dne-part-1
Signed-off-by: James Nunez <jnunez@whamcloud.com>
Change-Id: Ia8a1b3afcca7af645eed1d0f3dcf843e5254afe6
Reviewed-on: https://review.whamcloud.com/35263
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Emoly Liu <emoly@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>