all: consistently use cpu_profile as flag name (#895)
This is more a workaround since a transitive dependency has introduced a
global flag "cpuprofile", leading to a panic due to registring the flag
twice.
To make ourselves immune to this issue we can refactor our usages to use
a FlagSet, even for "main". This is a bigger and frankly inconvenient
change for a somewhat rare occurance. Instead we just rename our flag.
I feel comfortable renaming since this flag should only really be used
by Zoekt developers. There will be the issue that the flag will be shown
twice for commands, but I will report to the upstream repo about this
problem.
Test Plan: go get -u ./... && go run ./cmd/zoekt-git-index works