twister: Support --coverage-formats on lcov also

When using twister to generate coverage with the coverage tool lcov,
allow using --coverage-formats to pick if you want lcov or html,
defaulting to both. Picking html will also use lcov, since that is
required for geninfo.  This will allow callers to avoid the potentially
slow and disk intensive html reports if they only wanted the lcov info
file.

Signed-off-by: Jeremy Bettis <jbettis@google.com>