LU-1538 tests: standardize test script init - sanity

LU-1538 tests: standardize test script init - sanity

Standardize the initial Lustre test script initialization of the
test-framework.sh 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 PATH, NAME, TMP, LFS, LCTL
variable initialization, since it is already done in init_test_env().

Move MACHINEFILE into init_test_env().

Move get_lustre_env() to the end of init_test_env(). All test scripts
currently call init_test_env() and this move will allow all test
scripts to use the variables defined in get_lustre_env() without
having to modify the individual test scripts.

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

Lustre-change: https://review.whamcloud.com/34863
Lustre-commit: 8fa23490bb5fd0df2b1def8b14d51919abde6555

Signed-off-by: James Nunez <jnunez@whamcloud.com>
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I1ef6639bcb3eb5179bd44da13b35fd843c267156
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Wei Liu <sarah@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/41226
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>