More validate optimisation

[matthewrmshin]

(Continue the theme from #2312.)

Avoid usage of costly regular expressions - use cheaper string replace instead.
Avoid doing the same string replacement multiple times.

Result of profile-battery on complex-validate.

Version            Run            Elapsed Time (s)  CPU Time - Total (s)  Max Memory (kb)
master             complex suite  9.7               9.8                   73156.0        
more-validate-opt  complex suite  8.6               8.6                   72928.0        

[matthewrmshin]

Snippet from cylc validate --profile of the horrible suite mentioned in #2312.

On master:

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
    13594    0.293    0.000   44.521    0.003 lib/cylc/graph_parser.py:368(_families_all_to_all)
   175840    3.340    0.000   43.345    0.000 lib/cylc/graph_parser.py:408(_add_trigger)

On this branch:

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
    13594    0.120    0.000    1.997    0.000 lib/cylc/graph_parser.py:368(_families_all_to_all)
    13594    0.700    0.000    0.768    0.000 lib/cylc/graph_parser.py:395(_add_trigger)

[oliver-sanders]

A mere 97% reduction - looks good to me!

[hjoliver]

Nice. (sanitized "horrible" suite validation now sub 1-min on my laptop, down from 9.5 min).