Add JVM flags for more consistent (and typically faster) timing #437

[gkreitz]

Adds JVM command line options to:

• spend less CPU optimizing (this seems to yield a speed-up for the vast majority of submissions)
• pretend there's a fixed number of CPU cores, to get more consistent performance even when run on high core machines

Rejudging submissions on Kattis hardware, we had the following statistics when evaluating this change - the typical result is a quite significant speed-up, even if a few submissions do become slower.

--- Runtime by Language ---
Language       N    Med old    Med new    Med Δ    Geo ratio    p10 ratio    p90 ratio  >10% slower    >10% faster
----------  ----  ---------  ---------  -------  -----------  -----------  -----------  -------------  -------------
Java        1597      0.103      0.076   -0.022        0.711         0.46         0.89  54 (3%)        1465 (92%)
ALL         1597      0.103      0.076   -0.022        0.711         0.46         0.89  54 (3%)        1465 (92%)

--- Distribution of runtime ratio (new/old) ---
Ratio           Count  Percentage
------------  -------  ------------  ----------------------------------------
[0.00, 0.50)      214  13.4%         ############
[0.50, 0.80)      710  44.5%         ########################################
[0.80, 0.90)      532  33.3%         ##############################
[0.90, 0.95)       39  2.4%          ##
[0.95, 1.05)       40  2.5%          ##
[1.05, 1.10)        8  0.5%
[1.10, 1.25)       23  1.4%          #
[1.25, 2.00)       27  1.7%          ##
[2.00, ∞)           4  0.3%

Thanks @Tagl for raising the issue!

Fixes #437