opennebula: fix shell variables parsing

Fix parsing of the empty values written as:

KEY=""
KEY=''

Change-Id: I56ea03da5d78c01af2647444b825bf63d5146137

Author: ader1990

cloudbaseinit/metadata/services/opennebulaservice.py

@@ -88,12 +88,14 @@ def _parse_shell_variables(content):
         new_content = sep.join(lines)
         # get pairs
         pairs = {}
-        pattern = (br"(?P<key>\w+)=(['\"](?P<str_value>[\s\S]+?)['\"]|"
-                   br"(?P<int_value>\d+))(?=\s+\w+=)")
+        pattern = (br"(?P<key>\w+)=((?P<int_value>\d+)|"
+                   br"['\"](?P<str_value>[\s\S]*?)['\"])(?=\s+\w+=)")
         for match in re.finditer(pattern, new_content):
             key = encoding.get_as_string(match.group("key"))
-            pairs[key] = (match.group("str_value") or
-                          int(match.group("int_value")))
+            val = match.group("str_value")
+            if match.group("int_value"):
+                val = int(match.group("int_value"))
+            pairs[key] = val
         return pairs
 
     @staticmethod

cloudbaseinit/tests/metadata/services/test_opennebulaservice.py

@@ -145,13 +145,17 @@ def _test_parse_shell_variables(self, crlf=False, comment=False):
             d: e
             '
             ivar=10
+            TESTEMPTY=''
+            TESTEMPTY2=""
         """)
         if comment:
             content += "# A simple comment\n"
         if crlf:
             content = content.replace("\n", "\r\n")
         pairs = self._service._parse_shell_variables(content.encode())
         _pairs = {
+            "TESTEMPTY": b"",
+            "TESTEMPTY2": b"",
             "VAR1": b"1",
             "var2": b"abcdef",
             "VAR_VAR3": b"aaa.bbb.123.ccc",