Added functions to unset some env vars while building

The EasyBlock class now has a member unwanted_env_vars which has list of
environment variables to unset before building. They are restored after
the build completes.
Moved read_environment to tools/environment

Moved read_environment from tools/utilities to tools/environment.
Moved filetools/modify_env to tools.environment

Moved modify_env from tools/filetools to tools/environment
Updated old deprecated message for read_environment

Moved from config -> utilities -> environment
make sure we obtain the correct type of logger object (EasyBuildLog, not FancyLogger)
correct import statements for modify_env and read_environment (import from easybuild.tools.environment now)
fix typo
add unwanted_env_vars easyconfig parameter, as opposed to using EasyBlock class variable
Merge pull request #673 from wpoely86/change_env_vars

Unset & restoring environment variables functions for eb's
add support for updating list easyconfig values
Merge pull request #676 from boegel/update_lists

add support for updating list easyconfig values
Add --dry-run to eb per issue #654

Adds a --dry-run option to eb. When used, prints the list of
easyconfigs to be built and whether each one currently exists,
then exits. If --robot is used, also does this for each of their
dependencies.
initialize self.self.sanity_check_fail_msgs for extensions
Merge pull request #678 from boegel/sanity_check_fail_msgs

initialize self.self.sanity_check_fail_msgs for extensions
Fix --dry-run option per comments in PR

* Split dry-run out into a separate function
* Change output syntax to be more easily greppable
* Convert camelCase variables to snake_case
Merge pull request #677 from ajdecon/dryrun

Add --dry-run to eb per issue #654
Merge branch 'develop' into fix_list-toolchains
fix docstring