Improve test tag string parsing

Instead of just adding the missing -clx,
the new way aims to be forward compatible.

The new implementation is quite permissive,
ignoring all "word" chars sticking to the trigger word
and returning everything after that and space up to the endline.

+ Unified perftest and devicetest handling.
 + Consequently, triggers like "devicetest-1n-skx GBP" will work now.

Change-Id: I3bda6105195180d35a589a75318f569e36f03461
Signed-off-by: Vratko Polak <vrpolak@cisco.com>