Description of problem:

Currently the `host_pattern` for the `HostSpec` only allows limited filtering (it uses the fnmatch.filter() method internally - https://docs.python.org/3/library/fnmatch.html ). Optionally allowing something like `host_pattern_regex` via python `re` would allow our customers to use more sophisticated filters. 

Version-Release number of selected component (if applicable):

all 

How reproducible:

n/a

Expected results:

regex filtering for host_patterns

Additional info:

Current filtering:
~~~
python-common/ceph/deployment/service_spec.py:
def filter_matching_hostspects(...):
[...]
        if self.host_pattern:
            return fnmatch.filter(all_hosts, self.host_pattern)
[...]
~~~