Prevent apache exiting after failing to find a webroot.

An `exit 1` from the apache script aborts the entire provision, this isn't ideal.

Instead we now simply link the webroot if we find it, otherwise it remains

fixes #29
The alternatives are:

1. Always have a www folder (ie: include it in the repo)
1. exit 0 instead of 1 (because the exit 1 causes the entire provision to fail); though this is still nasty as other parts of the script won't run