pkg.list_upgrades: Ignore "downloading" lines in pacman output

It appears that Antergos distributes a modified version of pacman which
adds additional lines while updating its package databases. These are
incorrectly interpreted as available upgrades. This commit checks for
these lines in the output and skips them.

salt/modules/pacman.py

@@ -155,10 +155,17 @@ def list_upgrades(refresh=False, root=None, **kwargs):  # pylint: disable=W0613
         out = call['stdout']
 
     for line in salt.utils.itertools.split(out, '\n'):
-        comps = line.split(' ')
-        if len(comps) != 2:
+        try:
+            pkgname, pkgver = line.split()
+        except ValueError:
             continue
-        upgrades[comps[0]] = comps[1]
+        if pkgname.lower() == 'downloading' and '.db' in pkgver.lower():
+            # Antergos (and possibly other Arch derivatives) add lines when pkg
+            # metadata is being downloaded. Because these lines, when split,
+            # contain two columns (i.e. 'downloading community.db...'), we will
+            # skip this line to keep it from being interpreted as an upgrade.
+            continue
+        upgrades[pkgname] = pkgver
     return upgrades