Allow to keep the build dir after succesful build

Set the option cleanupbuild to False to keep the build dir after a
succesful build. Can be helpfull for debugging purposes.
Added intel & foss toolchains
add support for postinstallcmds, deprecate makeopts/premakeopts in favor of buildopts/prebuildopts
enhance unit tests w.r.t. postinstallcmds and deprecated makeopts
fix typo
fix checksums in unit tests
only warn about mismatch between provided build specs and available specs for easyconfig format v1.0
fix collaboration between --robot and --try-X
replace faulty use of tweak with tweak_one
extra check for finalpath being available
Use gcc -v instead of gcc --version

Gives more useful information
Make boegel happy by naming the argument.
include line mentioning tester in PR comment
Merge pull request #925 from boegel/test_reporter

include line mentioning tester in PR comment
Merge pull request #924 from wpoely86/gcc-v

use gcc -v
allow more liberal version regexp in EnvironmentModulesC

Older versions of environment modules (C) simply output version strings like `3.1.6`.  Make the VERSION_REGEXP accept this.
fix test_skip unit test (how the hell did this every work?!)
Revert "only warn about mismatch between provided build specs and available specs for easyconfig format v1.0"

This reverts commit ab9cd62f2eb4327af195a141ec2403b65adb762e.
only trickle down build specs when required/correct
fix 2nd part of test_skip, toy module should *not* be there in that case