Pre-build clean now removes submodule directories

src/external/tng_io is a submodule, and in order to clean it out for
future builds, a second -f flag to git clean is needed. This kind of
thing is a good idea because of the amount of globbing that our build
system does.

Change-Id: I4179188762fd063afe6093ac8b100fb5fbe2661b
Make Valgrind checks use /usr/local/bin/valgrind

Needed so that we can tune the version of the valgrind package that is
used (required >= 3.8), since (e.g.) Ubuntu 12.04 version of valgrind
(3.7.0) does not support AVX.

Change-Id: I065ffb1b5d621581db25082353d3528a2eb06e77
use NODE_NAME environment variable to determine node

Currently we depend on the host name being specified in the OPTIONS
variable. In case we decide to have a more flexible job configuration
at some point that might be a problem. We can use the environment
variable NODE_NAME instead. Jenkins sets this variable at runtime,
see http://jenkins.gromacs.org/env-vars.html/

Change-Id: I709f99bccecdd2cadf4c8bf6a7ac680dac129836
Revert "Make Valgrind checks use /usr/local/bin/valgrind"

Stefan made a package for valgrind 3.8.1, so this change is no longer required

This reverts commit 3037dc5ff5c174b046bf5389786368a87f77ce4a.

Change-Id: I94899d33363c452fa68fd5d60a6b7a46b0b4273d
Merge "Revert "Make Valgrind checks use /usr/local/bin/valgrind"" into 5.0.0
Merge "Pre-build clean now removes submodule directories" into 5.0.0