base/start: do not run circusd as root

sudo will strip some environment variables. Updated from my sudo:

  Environment variables to remove:
	RUBYOPT
	RUBYLIB
	PYTHONUSERBASE
	PYTHONINSPECT
	PYTHONPATH
	PYTHONHOME
	TMPPREFIX
	ZDOTDIR
	READNULLCMD
	NULLCMD
	FPATH
	PERL5DB
	PERL5OPT
	PERL5LIB
	PERLLIB
	PERLIO_DEBUG
	JAVA_TOOL_OPTIONS
	SHELLOPTS
	GLOBIGNORE
	PS4
	BASH_ENV
	ENV
	TERMCAP
	TERMPATH
	TERMINFO_DIRS
	TERMINFO
	_RLD*
	LD_*
	PATH_LOCALE
	NLSPATH
	HOSTALIASES
	RES_OPTIONS
	LOCALDOMAIN
	CDPATH
	IFS

Environments like PYTHONPATH, PYTHONHOME and RUBYOPTS could cause some
problem. We actually had troubles with the ENV environment variable.