20343: Define Python regexps with raw strings

20343: Define Python regexps with raw strings

Prevent the DeprecationWarning added to Python 3.6 for unrecognized
string escape sequences. Found candidates by running:

    git grep --line-number -E '\bre\.\w+\([^r]*\\'

Most of the changes just add the raw string prefix `r` to these regexps,
but I did make some other readability improvements while I was at it,
including switching from regexps to plain string test methods where
appropriate.

Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith@curii.com>