Bug 1392700 - Initialize repository using latest requirements. r=aki, a=test-only

We use hg init to create the directory. Because this is what
typically occurs.

We also remove the disabling of "dotencode" in the hgrc. This was added
in https://hg.mozilla.org/build/mozharness/rev/b1dbc0f56ff8 (bug 857853)
for reasons that are unclear to me. We should never disable dotencode
because it may make some repositories not clonable on Windows
filesystems.

Disabling dotencode will also interfere with the latest version of
robustcheckout, which requires its presence.

MozReview-Commit-ID: 35qBsgwp0uW