pmb.parse.parse_attribute: strip off trailing comment on attrib line (MR 2149)

The apkbuild parser could not handle cases where a line ends in a
comment but the value is not quoted.

E.g. this:

    pkgver=1.0 # I'm a comment, look at me

was being parsed to a value like this:

    1.0 # I'm a comment, look at me

... which is obviously wrong. This strips off any trailing comment on
the line, so it's parsed to the correct value.

fixes #2087

pmb/parse/_apkbuild.py

@@ -159,6 +159,7 @@ def parse_attribute(attribute, lines, i, path):
 
     # Single line
     if not end_char:
+        value = value.split("#")[0].rstrip()
         return (True, value, i)
     if end_char in value:
         value = value.split(end_char, 1)[0]