[cni] MAISTRA-2291 Support deployment of multiple plugin versions in Istio CNI

[bartoszmajsak]

Includes:

• MAISTRA-2135 Add unit tests for our CNI binary-prefix work (MAISTRA-2135 Add unit tests for our CNI binary-prefix work #325)

• MAISTRA-2137 Make network namespace setup executable name configurable (MAISTRA-2137 Make network namespace setup executable name configurable #273)

  To support the deployment of multiple CNI plugin versions, the name of the
  executable that is invoked to set up the network namespace must be configurable.

• OSSM-1430: CNI: Watch for modified files with a prefix (OSSM-1430: CNI: Watch for modified files with a prefix #510)

  Because our CNI pod contains more than one container, and they write to
  the same directory, and they watch for changes on those directories,
  changes made by one container trigger the watch on the other, which will
  responde by copying the files to the directory, which will in turn
  trigger the watcher of the other container in an endless loop.

  This leads to high CPU usage on the node.

  This PR changes the logic to only monitor for files that have the
  desired prefix. Thus, for example, the 2.2 container will only react to
  changes to files whose names start with "v2-2". This avoid this race
  condition and achieve the same end result.Please provide a description of this PR:

• MAISTRA-2051 use correct UID/GID in istio-iptables

• OSSM-2082 CNI installer now creates the net.d directory if necessary OSSM-2082 CNI installer now creates the net.d directory if necessary #638

[luksa]

LGTM, but we can probably simplify that temp dir stuff.