ceph-osd: restructure lvm_volumes variable for more flexiblity

ceph-osd: restructure lvm_volumes variable for more flexiblity

The lvm_volumes variable is now a list of dictionaries that represent
each OSD you'd like to deploy using ceph-volume. Each dictionary must
have the following keys: data, journal and data_vg. Each dictionary also
can optionaly provide a journal_vg key.

The 'data' key represents the lv name used for the OSD and the 'data_vg'
key is the vg name that the given lv resides on. The 'journal' key is
either an lv, device or partition. The 'journal_vg' key is optional and
must be the vg name for the journal lv if given. This key is mainly used
for purging of the journal lv if purge-cluster.yml is run.

For example:

  lvm_volumes:
    - data: data_lv1
      journal: journal_lv1
      data_vg: vg1
      journal_vg: vg2
    - data: data_lv2
      journal: /dev/sdc
      data_vg: vg1

Signed-off-by: Andrew Schoen <aschoen@redhat.com>