Type-test has_output instead of requiring pattern=True

[gvwilson]

Instead of has_output('some string', pattern=True), how about has_output(re.compile('some string')), i.e., use a type test inside has_output and apply the regex if one is given (match strings if not). This gets simpler if our code has:

from re import compile as rxc

so that the example above becomes has_output(rxc('some string')).