cephadm: use importlib.metadata for querying ceph_iscsi's version

use importlib.metadata for querying ceph_iscsi's version and fallback to
pkg_resources. as the former is only available in Python 3.8, while
the latter is deprecated.

Refs https://tracker.ceph.com/issues/66201
Signed-off-by: Kefu Chai <[email protected]>

Author: tchaikov

src/cephadm/cephadmlib/daemons/iscsi.py

@@ -136,6 +136,11 @@ def python(s: str) -> Tuple[str, str, int]:
         out, _, code = python(
             "from importlib.metadata import version; print(version('ceph_iscsi'))"
         )
+        if code == 0:
+            return out.strip()
+        out, _, code = python(
+            "import pkg_resources; print(pkg_resources.require('ceph_iscsi')[0].version)"
+        )
         if code == 0:
             return out.strip()
         return None