Change benchmarks run in CI job (#3388)
Change benchmarks run in CI job (#3388)

* Change benchmarks run in CI job

This commit changes up the benchmarks we run in the travis CI job. This
job is very susceptible to noise because of shifts in CI node
performance. The environment that travis uses to host their environment
has variable performance being that they run on public clouds so to
minimize spurious failures caused by things outside of our control we
should try to limit the benchmarks we run to smaller synthetic ones then
larger full path tests. To this end this commit removes the state
tomography benchmark and replaces it with synthetic benchmarks for
circuit construction, converters, and the assembler. The state
tomography benchmarks involves running a simulation with BasicAer,
ignis, and quantum_info to calculate the state fidelity and while this
is a useful benchmark in dedicated benchmarking environment there is too
much work going on to provide repeatable results for the CI job.

* Remove converters from list of ci benchmarks

This commit removes the converters benchmarks from the list while each
benchmark iteration takes at most a few seconds the matrix of benchmarks
run is quite large and the setup can be expensive for the larger
circuits. While it only takes a few extra minutes locally on a
reasonable system, in the slow ci nodes this pushes things beyond the
45min timeout. To make sure we have enough time budget this commit
removes the converter benchmarks from the list we run in ci.

* Remove QFT from list of benchmarks too

The qft benchmarks also run for a long time and suffer from the same
kind of variability that state_tomography did (although to a lesser
extent). This commit removes it from the list too.

* Add converter benchmarks for depth 8

Running the full range of benchmarks for the converter functions across
takes too much time (mostly in setup). But they can provide valuable
insights. This commit adds just the depth 8 versions of the benchmarks
to the list we run in CI. This should be a tradeoff of actually running
them but having it execute quickly enough in our ci env.

QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py