maintainers: move MAINTAINER parsing to module

In prep for supporting 'OWNERS' move maintainers parsing
details to the appropriate submodule.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I38aa703f36a82cc0ed34cc78d9ece76150f73b01
diff --git a/maintainers/obmc-gerrit b/maintainers/obmc-gerrit
index db6bcfe..b666652 100755
--- a/maintainers/obmc-gerrit
+++ b/maintainers/obmc-gerrit
@@ -24,23 +24,11 @@
     reviewers: List[str] = list()
     if not root:
         root = git("rev-parse", "--show-toplevel").strip()
+
     mfile = os.path.join(root, mname)
-    if not os.path.exists(mfile):
-        return (maints, reviewers)
-    with open(mfile, "r") as mstream:
-        maintainers.trash_preamble(mstream)
-        block = maintainers.parse_block(mstream)
-        if not block:
-            return (maints, reviewers)
-        mlist = cast(
-            List[maintainers.Identity], block[maintainers.LineType.MAINTAINER]
-        )
-        maints.extend(i.email.address for i in mlist)
-        if maintainers.LineType.REVIEWER in block:
-            rlist = cast(
-                List[maintainers.Identity], block[maintainers.LineType.REVIEWER]
-            )
-            reviewers.extend(i.email.address for i in rlist)
+    if os.path.exists(mfile):
+        return maintainers.get_reviewers(mfile)
+
     return (maints, reviewers)