Fix version string parsing of terra (#1135)

In the upcoming terra release there will be a release candidate tagged
prior to the final release. However changing the version string for the
package is blocked on the ibmq provider right now because it is trying
to parse the version and is assuming there will be no prelease suffix on
the version string (see Qiskit/qiskit#8200 for the details). This
commit fixes this version parsing to use the regex from the
pypa/packaging project which handles all the PEP440 package versioning
include pre-release suffixes. This will enable terra to release an
0.21.0rc1 tag without breaking the ibmq provider.

Co-authored-by: Rathish Cholarajan <rathishc24@gmail.com>

qiskit/providers/ibmq/runtime/utils.py

@@ -21,6 +21,7 @@
 import inspect
 import io
 import json
+import re
 import warnings
 import zlib
 from datetime import date
@@ -47,7 +48,52 @@
 
 from qiskit.version import __version__ as _terra_version_string
 
-_TERRA_VERSION = tuple(int(x) for x in _terra_version_string.split(".")[:3])
+
+# This version pattern is taken from the pypa packaging project:
+# https://github.com/pypa/packaging/blob/21.3/packaging/version.py#L223-L254
+# which is dual licensed Apache 2.0 and BSD see the source for the original
+# authors and other details
+VERSION_PATTERN = (
+    "^"
+    + r"""
+    v?
+    (?:
+        (?:(?P<epoch>[0-9]+)!)?                           # epoch
+        (?P<release>[0-9]+(?:\.[0-9]+)*)                  # release segment
+        (?P<pre>                                          # pre-release
+            [-_\.]?
+            (?P<pre_l>(a|b|c|rc|alpha|beta|pre|preview))
+            [-_\.]?
+            (?P<pre_n>[0-9]+)?
+        )?
+        (?P<post>                                         # post release
+            (?:-(?P<post_n1>[0-9]+))
+            |
+            (?:
+                [-_\.]?
+                (?P<post_l>post|rev|r)
+                [-_\.]?
+                (?P<post_n2>[0-9]+)?
+            )
+        )?
+        (?P<dev>                                          # dev release
+            [-_\.]?
+            (?P<dev_l>dev)
+            [-_\.]?
+            (?P<dev_n>[0-9]+)?
+        )?
+    )
+    (?:\+(?P<local>[a-z0-9]+(?:[-_\.][a-z0-9]+)*))?       # local version
+"""
+    + "$"
+)
+_TERRA_VERSION = tuple(
+    int(x) for x in re.search(
+        VERSION_PATTERN,
+        _terra_version_string,
+        re.VERBOSE | re.IGNORECASE
+    ).group("release").split(".")
+)
 
 
 def to_base64_string(data: str) -> str: