perf monitoring for CBT runs

[harriscr]

Code to provide monitoring using the perf tool of CBT runs already exists in the codebase. It was only set up to monitor OSDs and had some requirements that meant it would only run on clusters that used vstart.
#357 split the top monitoring, which was in the same format, into 2 separate classes: One for generic top monitoring, and one specifically for OSDs using vstart (so as not to break the existing behaviour). We can apply the same division of responsibility to perf monitoring.

This also adds checking to monitoring, so that if a monitoring tool requested in the yaml is not installed then CBT will exit with an error. The exception is collectl, which has a default set of options. If collectl is not inslaeed then a warning os written and the CBT run will continue.

Additional unit tests were added for the new code where appropriate.

This has been tested by running on a local system:

ls cbt_runs/results/00000000/id-94a6db48/seq32kread.cephalasquad3.ssd.hursley.ibm.com/rbdfio/numjobs-001/iodepth-000192/
collectl       json_output.3  json_output.7        output.0_iops.1.log  output.1_bw.1.log    output.1_slat.1.log  output.2_iops.1.log  output.3_bw.1.log    output.3_slat.1.log  output.4_iops.1.log  output.5_bw.1.log    output.5_slat.1.log  output.6_iops.1.log  output.7_bw.1.log    output.7_slat.1.log
json_output.0  json_output.4  output.0             output.0_lat.1.log   output.1_clat.1.log  output.2             output.2_lat.1.log   output.3_clat.1.log  output.4             output.4_lat.1.log   output.5_clat.1.log  output.6             output.6_lat.1.log   output.7_clat.1.log  perf
json_output.1  json_output.5  output.0_bw.1.log    output.0_slat.1.log  output.1_iops.1.log  output.2_bw.1.log    output.2_slat.1.log  output.3_iops.1.log  output.4_bw.1.log    output.4_slat.1.log  output.5_iops.1.log  output.6_bw.1.log    output.6_slat.1.log  output.7_iops.1.log  top
json_output.2  json_output.6  output.0_clat.1.log  output.1             output.1_lat.1.log   output.2_clat.1.log  output.3             output.3_lat.1.log   output.4_clat.1.log  output.5             output.5_lat.1.log   output.6_clat.1.log  output.7             output.7_lat.1.log   visualisation

and

ls cbt_runs/results/00000000/id-94a6db48/seq32kread.cephalasquad3.ssd.hursley.ibm.com/rbdfio/numjobs-001/iodepth-000192/perf/
perf.data

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