Merge pull request #507 from euanh/opam

opam: Add documentation and remove opam-installer
opam: Put back opam-installer!

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #508 from euanh/opam

opam: Put back opam-installer!
opam: Fix typo in changelog

Signed-off-by: Euan Harris <euan.harris@citrix.com>
opam: Add build dependency on curl

We use the full release tarball so no sources have to be downloaded,
but the configure script fails if curl is not installed.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
rpm/configure.sh: Remove unnecessary directories

These were introduced in change 18c6b647 to support
storing Mock's cache and chroot in the workspace.
Most of this was reverted in commit abc1705b.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
rpm/configure.sh: Tidy up script

Signed-off-by: Euan Harris <euan.harris@citrix.com>