use new uberenv + spack

[cyrush]

No description provided.

[coveralls]

Coverage remained the same at 86.326% when pulling 815a835 on task/2021_01_update_uberenv into 1b012af on develop.

[cyrush]

almost there, but currently blocked by:
spack/spack#22530

[cyrush]

Error in Docker test:

ImportError: /conduit/uberenv_libs/spack/opt/spack/linux-ubuntu18.04-broadwell/gcc-7.5.0/python-3.8.8-rcva2ue7focsi7wr3ayizkg327hrcmfy/lib/python3.8/site-packages/mpi4py/MPI.cpython-38-x86_64-linux-gnu.so: undefined symbol: MPI_UNWEIGHTED

fixed, there were two mpis in play due to a mixup with how the container was setup.

[cyrush]

error in other tests:

[activating dependent packages] 
[ERROR: failed to find package named 'uberenv-conduit']

uberenv shouldn't be trying to activate this package, looking into it ...

This is confusing b/c the error is not related to activating, it happens later.
Adding some better status to uberenv to avoid future tail chasing.

[cyrush]

this is ready + ci test for newer cmake in #747 requires this, so I am merging.