python: mark regex strings with 'r' prefix

python: mark regex strings with 'r' prefix

When writing regexes special regex matches like "\d" can get
misinterpreted as normal string escape sequences:

docs/apibuild.py:1359:51: W605 invalid escape sequence '\d'
                        value = value + re.sub("^(\d+)U$", "\\1", token[1])
                                                  ^
docs/apibuild.py:2134:31: W605 invalid escape sequence '\('
                m = re.match("\(?1<<(\d+)\)?", info[0])
                              ^
docs/apibuild.py:2134:38: W605 invalid escape sequence '\d'
                m = re.match("\(?1<<(\d+)\)?", info[0])
                                     ^
docs/apibuild.py:2134:42: W605 invalid escape sequence '\)'
                m = re.match("\(?1<<(\d+)\)?", info[0])
                                         ^

To avoid this probem all regexes should use the r"...." syntax for their
strings, which disables normal string escape sequences.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>