Bump FileWatching tolerances

[staticfloat]

It's very difficult to know if these are actually sufficient, but I guess we'll see if things improve. Two fixes here; the first is for #26725; it puts a sleep within a for loop so that there's some space in between rm() calls. We'll see if this actually has any effect other than adding a few tenths of a second to our test suite. The second is for #27287 to generally bump all time thresholds from 0.3 seconds up to 0.5, as our windows buildbot fs performance while under load is so bad that we need it that high.

[mbauman]

Travis Win32 failed with a GC segfault in bidiag, 64bit CircleCI was OOM killed during compilation.