Expand mamba usage for base and environment installs
Expand mamba usage for base and environment installs

Attempt to improve bcbio install speeds (bcbio/bcbio-nextgen#3054
bcbio/bcbio-nextgen#3062) by general usage of mamba throughout.

After testing, we could refactor code in _initial_base_install
to be shorter.

If more speed improvements are needed, we could perhaps avoid
second conda install after mamba, which we're including now to
avoid any mamba specific resolve issues.

chapmanb/cloudbiolinux,chapmanb/cloudbiolinux,chapmanb/cloudbiolinux,chapmanb/cloudbiolinux