git: clean up "fetch" method

De-duplicate repetitive code checking the exit code.

Include the stdout/stderr of the failed process in all cases.

Remove the returned values because no caller uses them.

Combine git commands where possible.  There is no need to fetch branches
and tags as two separate operations.

lib/ansible/modules/source_control/git.py

@@ -453,33 +453,20 @@ def get_head_branch(git_path, module, dest, remote, bare=False):
 
 def fetch(git_path, module, repo, dest, version, remote, bare):
     ''' updates repo from remote sources '''
-    out_acc = []
-    err_acc = []
-    (rc, out0, err0) = module.run_command([git_path, 'remote', 'set-url', remote, repo], cwd=dest)
-    if rc != 0:
-        module.fail_json(msg="Failed to set a new url %s for %s: %s" % (repo, remote, out0 + err0))
-    if bare:
-        (rc, out1, err1) = module.run_command([git_path, 'fetch', remote, '+refs/heads/*:refs/heads/*'], cwd=dest)
-    else:
-        (rc, out1, err1) = module.run_command("%s fetch %s" % (git_path, remote), cwd=dest)
-    out_acc.append(out1)
-    err_acc.append(err1)
-    if rc != 0:
-        module.fail_json(msg="Failed to download remote objects and refs: %s %s" %
-                (''.join(out_acc), ''.join(err_acc)))
+    commands = [["set a new url %s for %s" % (repo, remote)], [git_path, 'remote', 'set-url', remote, repo]]
+
+    fetch_str = 'download remote objects and refs'
 
     if bare:
-        (rc, out2, err2) = module.run_command([git_path, 'fetch', remote, '+refs/tags/*:refs/tags/*'], cwd=dest)
+        refspecs = ['+refs/heads/*:refs/heads/*', '+refs/tags/*:refs/tags/*']
+        commands.append([fetch_str, [git_path, 'fetch', remote] + refspecs])
     else:
-        (rc, out2, err2) = module.run_command("%s fetch --tags %s" % (git_path, remote), cwd=dest)
-    out_acc.append(out2)
-    err_acc.append(err2)
-    if rc != 0:
-        module.fail_json(msg="Failed to download remote objects and refs: %s %s" %
-                (''.join(out_acc), ''.join(err_acc)))
-
-    return (rc, ''.join(out_acc), ''.join(err_acc))
+        commands.append([fetch_str, [git_path, 'fetch', '--tags']])
 
+    for (label,command) in commands:
+        (rc,out,err) = module.run_command(command, cwd=dest)
+        if rc != 0:
+            module.fail_json(msg="Failed to %s: %s %s" % (label, out, err))
 
 def submodules_fetch(git_path, module, remote, track_submodules, dest):
     changed = False