create-dev-env.sh:  if run from repo, set $BASE appropriately

2 changes:
[1] If PROJECT_HOME is not set, AND create-dev-env.sh is run from a cloned repo, then set BASE to that repo;
else:  (and only finally) set BASE to a default of "$HOME/edx_all"

[2] if PROJECT_HOME is set, or if this is from a repo, don't add edx_all to the BASE name (no need;)
Install: Fix use of DEBIAN_FRONTEND - `sudo` clears environment

Before executing a command, for security reasons `sudo` clears the
environment, so the value of DEBIAN_FRONTEND was never passed to
apt-get. This was causing the mysql packqge to still prompt for
a value interactively.
Install: Options "-q" (quiet), "-n" (no pull), "-y" (non interactive)

Added several options to the `create-dev-env.sh` script to improve its
ability to be used by another script:

* -y -- non interactive mode (no prompt, proceed immediately)
* -n -- do not attempt to pull edx-platform
* -q -- be more quiet (removes info at beginning & end)

This will be used, in particular, for Vagrant provisioning.
Install: Improves ruby/rvm install - Directly install the right version

The script used to download the latest version of ruby through rvm, then
later on install the one used by the project. Now we directly download
the version of the project when rvm is installed.
Install: Make curl options more consistent, add logging of errors

The options passed to curl were not always the same - added logging of
error (-S) everywhere (was only used for Mac before) and made it quiet
in the rare few cases where it wasn't yet (-s).
Install: Make `apt-get` and `mkvirtualenv` output log friendly

Added options to make the output of `apt-get` and `mkvirtualenv`
friendlier to getting logged. This allows to be more easily recorded in
log files or when the install is performed through utilities - like
Vagrant.
Install: Fix install script freeze (syncdb superuser account creation)

Since the output is passed through tee, when the django admin asks the
user if he would like to create a super user account, it blocks the
install, without even showing the question.

Disabled interactivity for syncdb.
Vagrant: Add support for Vagrant install (`vagrant up`)

Cf README, this adds support to install and setup a dev instance through
Vagrant. The Vagrantfile at the root handles the vagrant commands like
`vagrant up`.

Provisioning is done by the shell script `vagrant-provisionning.sh`,
which is a light wrapper around the `create-dev-setup.sh` which does
most of the job using the standard process, but limiting possible
side-effect by ensuring the environment on which the install is
performed is clean.

Based on an Ubuntu precise 12.04 LTS.