webtry: Simplify the directory where we check it out.

It does not need to be redundant, i.e. (~/buildbot/buildbot/), as it is
currently. It can be just ~/buildbot by just passing '--name .' to
'gclient config'.

Tested with the following command lines:

$ cd somewhere
$ mkdir buildbot
$ cd buildbot
$ gclient config --name . --unmanaged https://skia.googlesource.com/buildbot.git
$ gclient sync

Also --unmanaged was added to both 'gclient config' command lines (for
skia and buildbot) because otherwise gclient will create a .gclient file
with "managed" parameter set to true, but was long ago deprecated.
Also '--unmanaged' is the recommended way for checking out skia code as
outlined in the skiadocs
(https://sites.google.com/site/skiadocs/user-documentation/downloading).

Changed to 'git clone' because we don't need common or any third_party deps in the buildbot repo for webtry server to work. According to Eric (borenet), plain git commands are preferred.

BUG=None
TEST=see above
R=humper@google.com

Review URL: https://codereview.chromium.org/744463005
Fix doc typos in metadata package.

From
https://skia.googlesource.com/buildbot/+/170a31271e4ae797ac46755e80f84129701fd6e8

BUG=None
TBR=jcgregorio@google.com

Review URL: https://codereview.chromium.org/786193005