Switch to use yum installing RPM packages.

Refs #10613
Assume 'yes' for yum install of mantid.

Refs #10613
Set dynamic library path on Windows/OSX before running system tests.

Ensures that the tests find the correct Mantid libraries and 3rd party
components.
Refs #10816
Merge pull request #8 from mantidproject/bugfix/10816_fix_loader_search_path

Set dynamic library path on Windows/OSX before running system tests.
Merge pull request #6 from mantidproject/feature/10613_use_yum_systemtests

Use yum in package installer for rpm