feat: `AIX` related fixes and manually limit `AWR` usage period

[wpuziewicz]

This PR does the following Oracle changes:

• Add option limit AWR collection window of performance stats to 7 days.
• Use 'N/A' for md5 hash in manifest file if md5sum binary is not installed.
• Suppress error message if md5sum is not installed.
• Change method of checking user privileges.
• Remove parenthesis for ksh compatibility.

[cofin]

Re: the manifest file. Is it possible to exclude the checksum from the manifest so that we still have one created?

[wpuziewicz]

Will update to just use "N/A" as the hash value if the md5sum binary is not available.