Apply usual parameter encoding logic to method[request] parameter too.

Amends fbd62569bca926fc12917eb60eada82a6d8a83b0

Fixes:

encountered object 'Arvados::ResourceProxy=HASH(0x31fb2f8)', but neither allow_blessed nor convert_blessed settings are enabled at arvados/sdk/perl/lib/Arvados/Request.pm line 42.