Improve "error_text" message in query prepare

• The &mgm.errmsg= parameter is specific to EOS (dCache has no concept of mgm). Therefore, we have to change this parameter if we want to use it.
• We need to confirm if the message body sent back to EOS contains any field with the error information. If so, we may not need to use the &mgm.errmsg= parameter.
• The &mgm.errmsg= part of the issue can be handled in a separate ticket. There is no need to mix it with the formatting of the "error_text" message.

Add system tests for admin commands

• Will be handled by Pablo.

FST checksum metadata error leads to whole archive batch failing

• Jaroslav will take care of it (also to get familiar with EOS part of CTA system). A new dev ticket will be created.
• We need to understand what is causing the race condition.

cta-taped deceiving read performance

• The problem - 2 second delay between file reads - is only visible with small files (for large files it becomes irrelevant).
• Vlado will check with experts about what is the underlying scsi problem.

Large number of CRITICAL errors in cta-taped - "In BackendPopulator::~BackendPopulator(): error deleting agent (cta::exception::Exception). Backtrace follows."

• Issue #1020.
• Lasse will try to continue debugging with, and also use it to learn better how the object store works.