twister: More restrictive regex for log markers

Some simulators - like simics - may end up adding extraneous suffixes to
logged lines. This may cause some regex that match too much fail. This
patch fixes two such cases:

  - regex to find RunID changed to only match valid hexadecimal
    characters;
  - regex to match start of testsuite changed to only match valid word
    characters (0-9A-Za-z_).

Signed-off-by: Ederson de Souza <ederson.desouza@intel.com>