Clean up EclRun

[berland]

This is an epic for a clean-up of class EclRun.

Subtasks include

• Remove legacy functionality that bypasses vendor provided downstream eclrun
• Rename to reflect that is now purely a wrapper of downstream eclrun
• Remove MPI capabilities of ecl_run #8924 , this is handled by downstream eclrun
• Refactor to share code with a similar wrapper for running Flow
• In light of Eclipse version validation blocks custom ECLX00_SITE_CONFIG #9474, add a test and document a way to run a custom eclrun. Update: This is a matter of adding SETENV ECLRUN_PATH in the config, which is close enough to self-explanatory given the presence of that env variable.

Important features that are to be provided by the revamped wrapper:

• Retry in case of license issues (not relevant for Flow). Use existing code.
• Wait for UNSMRY-file to stabilize in size for MPI-runs (making MPI on NFS more robust). Share code with Flow wrapper. Refactor and rename summary_block() #8927
• Provide option to ignore errors from Eclipse. Share code with Flow
• Convert summary to hdf5 is user so wishes. Unsure if relevant for Flow.
• Relay environment variables from site-config to eclrun environment, or Make it possible to register PATH additions for forward models through plugin system #8967, or Allow pluginsystem to configure general key-value pairs pr forward model step #9036
• Special case PATH (augmentation) for the eclrun environment, maybe Make it possible to register PATH additions for forward models through plugin system #8967, or Allow pluginsystem to configure general key-value pairs pr forward model step #9036