t/perf/fsmonitor: initialize test with git reset

t/perf/fsmonitor: initialize test with git reset

Previously, the git add of the previous suiterun would
pollute the numbers in the second run

Before:
Test                                                          this tree
-----------------------------------------------------------------------------
7519.4: status (fsmonitor=fsmonitor-watchman)                 0.40(0.36+0.04)
7519.5: status -uno (fsmonitor=fsmonitor-watchman)            0.19(0.12+0.07)
7519.6: status -uall (fsmonitor=fsmonitor-watchman)           1.36(0.74+0.61)
7519.7: diff (fsmonitor=fsmonitor-watchman)                   0.14(0.10+0.04)
7519.8: diff -- 0_files (fsmonitor=fsmonitor-watchman)        0.14(0.10+0.04)
7519.9: diff -- 10_files (fsmonitor=fsmonitor-watchman)       0.14(0.09+0.05)
7519.10: diff -- 100_files (fsmonitor=fsmonitor-watchman)     0.14(0.10+0.04)
7519.11: diff -- 1000_files (fsmonitor=fsmonitor-watchman)    0.14(0.08+0.06)
7519.12: diff -- 10000_files (fsmonitor=fsmonitor-watchman)   0.14(0.10+0.04)
7519.13: add (fsmonitor=fsmonitor-watchman)                   2.03(1.28+0.69)
7519.16: status (fsmonitor=disabled)                          0.64(0.49+0.90)
7519.17: status -uno (fsmonitor=disabled)                     1.15(0.92+1.00)
7519.18: status -uall (fsmonitor=disabled)                    2.32(1.46+1.55)
7519.19: diff (fsmonitor=disabled)                            1.44(1.12+1.76)
7519.20: diff -- 0_files (fsmonitor=disabled)                 0.11(0.07+0.05)
7519.21: diff -- 10_files (fsmonitor=disabled)                0.11(0.06+0.05)
7519.22: diff -- 100_files (fsmonitor=disabled)               0.11(0.08+0.03)
7519.23: diff -- 1000_files (fsmonitor=disabled)              0.11(0.08+0.04)
7519.24: diff -- 10000_files (fsmonitor=disabled)             0.12(0.06+0.07)
7519.25: add (fsmonitor=disabled)                             2.25(1.47+1.47)

After:
Test                                                          this tree
-----------------------------------------------------------------------------
7519.4: status (fsmonitor=fsmonitor-watchman)                 0.41(0.33+0.09)
7519.5: status -uno (fsmonitor=fsmonitor-watchman)            0.20(0.14+0.07)
7519.6: status -uall (fsmonitor=fsmonitor-watchman)           1.37(0.78+0.58)
7519.7: diff (fsmonitor=fsmonitor-watchman)                   0.14(0.10+0.04)
7519.8: diff -- 0_files (fsmonitor=fsmonitor-watchman)        0.14(0.08+0.06)
7519.9: diff -- 10_files (fsmonitor=fsmonitor-watchman)       0.14(0.09+0.05)
7519.10: diff -- 100_files (fsmonitor=fsmonitor-watchman)     0.14(0.10+0.05)
7519.11: diff -- 1000_files (fsmonitor=fsmonitor-watchman)    0.14(0.11+0.04)
7519.12: diff -- 10000_files (fsmonitor=fsmonitor-watchman)   0.14(0.09+0.05)
7519.13: add (fsmonitor=fsmonitor-watchman)                   2.04(1.27+0.71)
7519.16: status (fsmonitor=disabled)                          0.78(0.59+0.99)
7519.17: status -uno (fsmonitor=disabled)                     0.43(0.32+0.88)
7519.18: status -uall (fsmonitor=disabled)                    1.58(0.96+1.38)
7519.19: diff (fsmonitor=disabled)                            0.36(0.31+0.79)
7519.20: diff -- 0_files (fsmonitor=disabled)                 0.11(0.08+0.03)
7519.21: diff -- 10_files (fsmonitor=disabled)                0.11(0.07+0.04)
7519.22: diff -- 100_files (fsmonitor=disabled)               0.11(0.08+0.04)
7519.23: diff -- 1000_files (fsmonitor=disabled)              0.11(0.07+0.05)
7519.24: diff -- 10000_files (fsmonitor=disabled)             0.12(0.08+0.05)
7519.25: add (fsmonitor=disabled)                             2.25(1.48+1.47)

Signed-off-by: Nipunn Koorapati <redacted>
Signed-off-by: Junio C Hamano <redacted>