As it is expected that the process collector can fail under certain
conditions (proc information for a process only readable by root or
other user for example) and as there is currently no option to configure
the error behavior of the client, this change reverts the error
reporting introduced in 159e96f. This effectively means that errors are
simply ignored and there won't be any samples for the process_* metrics
in case of an error.
Once a user can control how to behave in case of errors returned by
collectors, this change should probably be reverted.
The procfs package has a cgo dependency (necessary to calculate system
times). As procfs is not available under windows, darwin and supposely
all newer BSD systems, this change remove the procfs dependency on these
systems.