osmo_interact: improve vty transcript language by a regular rexex

Currently the transcript language understand 3 different tokens:
... (ignore all lines until the following line matches)
... !REGEX (ignore all lines except REXEX)

But to support osmo-stp with different compile options, the
vty help is indented with different amount of spaces depending on the compile options.
To support those add a regular regex using the prefix !r!

E.g.
```
OsmoSTP(config-cs7-as)# ?
-  description       Save human-readable description of the object
vs
+  description               Save human-readable description of the object
```

To use the new regex, the line would be:
```
!r!  description[ ]+Save human-readable description of the object
```

Further all regex special characters needs to be escaped.
```
  description   Save human-readable description of the object (for humans)

!r!  description[ ]+Save human-readable description of the object \(for humans\)
```

Change-Id: Iadcd7a8c3677548a6405e098fe53d0614ef2012c

Author: lynxis

osmopy/osmo_interact/common.py

@@ -218,14 +218,28 @@ def match_lines(expect, got):
         - If an 'expect' line is '... !regex', it matches any number of
           lines like '...', but the given regex must not match any of those
           lines.
+        - If the line starts with '!r!' following the regex, but a exact
+          match has priority
 
         Return 'True' on match, or a string describing the mismatch.
         '''
-        def match_line(expect_line, got_line):
-            return expect_line == got_line
 
         ANY = '...'
         ANY_EXCEPT = '... !'
+        REGEX = '!r!'
+
+        def match_line(expect_line, got_line):
+            if expect_line == got_line:
+                return True
+
+            # try to parse the expect_line as regex
+            if expect_line.startswith(REGEX):
+                try:
+                    if re.compile(expect_line[len(REGEX):]).match(got_line):
+                        return True
+                except:
+                    pass
+            return False
 
         e = 0
         g = 0