Fix double run of conda/mamba.
Fix double run of conda/mamba.

Thanks so much to @lbeltrame who found this issue, no wonder why
install times have been taking forever.

Closes #374. Closes bcbio/bcbio-nextgen#3395.

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