fix(instance-maanger): add ldflags when building instance manager

[ChanYiLin]

ref: longhorn/longhorn#8094

0. We are now checking out latest instance-manager when buiding instance-manager inside longhorn-engine here
1. When users manually exec longhorn-instance-manager inside longhorn-engine image, they will encounter

longhorn-instance-manager: error while loading shared libraries: libqcow.so.1: cannot open shared object file: No such file or directory

2. Fixed it by adding ldflags so the binary can find the lib
3. Since we validate engine binary path here, we have to soft link the binary inside the container to the tmp path, so the manual script can work.

[innobead]

@mergify backport v1.6.x

[mergify]

backport v1.6.x

🟠 Waiting for conditions to match

• merged [📌 backport requirement]

[ChanYiLin]

Our integration test intentionally test creation with invalid binary
Under current implementation, we won't return grpc error, instead we show the process status as failed and unregister the process
So we can modify the test and only validate the process list is empty in integration test

[innobead]

@ChanYiLin PR check failed. Need to fix it.

[ChanYiLin]

I don't know why this PR is disconnected with my branch
I can update the commit here by pushing new commit to my branch
I will recreate one