t/perf/p7519-fsmonitor.sh: warm cache on first git status

The first git status would be inflated due to warming of filesystem cache. This makes the results comparable. Before Test this tree -------------------------------------------------------------------------------- 7519.2: status (fsmonitor=.git/hooks/fsmonitor-watchman) 2.52(1.59+1.56) 7519.3: status -uno (fsmonitor=.git/hooks/fsmonitor-watchman) 0.18(0.12+0.06) 7519.4: status -uall (fsmonitor=.git/hooks/fsmonitor-watchman) 1.36(0.73+0.62) 7519.7: status (fsmonitor=) 0.69(0.52+0.90) 7519.8: status -uno (fsmonitor=) 0.37(0.28+0.81) 7519.9: status -uall (fsmonitor=) 1.53(0.93+1.32) After Test this tree -------------------------------------------------------------------------------- 7519.2: status (fsmonitor=.git/hooks/fsmonitor-watchman) 0.39(0.33+0.06) 7519.3: status -uno (fsmonitor=.git/hooks/fsmonitor-watchman) 0.17(0.13+0.05) 7519.4: status -uall (fsmonitor=.git/hooks/fsmonitor-watchman) 1.34(0.77+0.56) 7519.7: status (fsmonitor=) 0.70(0.53+0.90) 7519.8: status -uno (fsmonitor=) 0.37(0.32+0.78) 7519.9: status -uall (fsmonitor=) 1.55(1.01+1.25) Signed-off-by: Nipunn Koorapati <nipunn@dropbox.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>