cephadm: Refactor bootstrap.yml

[markgoddard]

Some tasks in bootstrap.yml go beyond the initial bootstrap, and may be
required if configuration changes or new hosts are added.

This change separates out configuration tasks into config.yml, and
cluster specification tasks into cluster.yml.

[markgoddard]

I haven't tested this, just wanted opinions on the approach.

[mnasiadka]

Looks good, but it would be nice to test it somewhere.

[cityofships]

Getting:

ERROR! Error when evaluating variable in import path: pkg_{{ ansible_os_family | lower }}.yml.

When using static imports, ensure that any variables used in their names are defined in vars/vars_files
or extra-vars passed in from the command line. Static imports cannot use variables from facts or inventory
sources like group or host vars.