upmap-remapped.py : Issues with python 3

[gillarda]

Hello,
First of all, thank you for this script !
I had a few issues running the script with python 3 on Centos 7.

$ python3 -V
Python 3.6.8

1. Error loading remapped pgs

$ python3 scripts/upmap-remapped.py
Error loading remapped pgs

The output of subprocess.check_output is of type byte, so it needs to be decoded before being able to use split:

for line in subprocess.check_output(['ceph', 'osd', 'pool', 'ls', 'detail']).split('\n'):

2. OSDS is not a list
   For the same reason, OSDS is byte and not list :

OSDS = subprocess.check_output(['ceph', 'osd', 'ls', '-f', 'json'])

3. Harmful cast in valid_osds
   Casting osds to str is useless and breaks the lookup in :

def valid_osds(osds):
  valid = []
  for osd in osds:
    if str (osd) in OSDS:
      valid.append(osd)
  return valid

I'll submit a PR with the various fixes.