aws/session: Skip shared config on read errors (#883)
aws/session: Skip shared config on read errors (#883)

Make it skip shared config file if it can't be read for
whatever reason (not exist, permissions, IO error, etc).

Previously files were skipped only if they didn't exist,
but other conditions can prevent them from being read and
same logic should be applicable to them.
agworld/aws-sdk-go,zmarois/aws-sdk-go,yxd-hde/aws-sdk-go,radeksimko/aws-sdk-go,xibz/aws-sdk-go,radeksimko/aws-sdk-go,yxd-hde/aws-sdk-go,myshen/aws-sdk-go,xibz/aws-sdk-go,yxd-hde/aws-sdk-go,zmarois/aws-sdk-go,calgaryscientific/aws-sdk-go,yxd-hde/aws-sdk-go,radeksimko/aws-sdk-go,zmarois/aws-sdk-go,myshen/aws-sdk-go,xibz/aws-sdk-go,calgaryscientific/aws-sdk-go,radeksimko/aws-sdk-go,calgaryscientific/aws-sdk-go,agworld/aws-sdk-go,agworld/aws-sdk-go,myshen/aws-sdk-go,myshen/aws-sdk-go,calgaryscientific/aws-sdk-go,zmarois/aws-sdk-go,xibz/aws-sdk-go,jasdel/aws-sdk-go,aws/aws-sdk-go,agworld/aws-sdk-go