replace loopsleepms with bash loadable

[paulfantom]

Summary

Simplify codebase by using bash loadable sleep for high-precision sleep instead of using custom shell wrapper.

Fixes #5161

Component Name

collectors/charts.d.plugin
collectors/tc.plugin

Additional Information

[paulfantom]

review anyone?

[ktsaou]

The sleep bash module is not available everywhere.
For example, it is not available in our static binaries.

The result of the removal of loopsleepms will be 2 forks per second for tc-qos-helper.sh and charts.d.plugin.

loopsleepms uses several alternative methods to eliminate the need for these forks:

1. /proc/uptime instead of external date
2. bultin sleep instead of external sleep
3. builtin read instead of external sleep

Issue #5161 is probably wrong. loopsleepms already uses the bash module when it is available:

netdata/collectors/charts.d.plugin/loopsleepms.sh.inc

Lines 111 to 131 in d0d109e

	if [ -z "${mysleep}" -a "$((BASH_VERSINFO[0] + 0))" -ge 3 -a "${NETDATA_BASH_LOADABLES}" != "DISABLE" ]; then
	# enable modules only for bash version 3+
	for bash_modules_path in ${BASH_LOADABLES_PATH//:/ } "$(pkg-config bash --variable=loadablesdir 2>/dev/null)" "/usr/lib/bash" "/lib/bash" "/lib64/bash" "/usr/local/lib/bash" "/usr/local/lib64/bash"; do
	[ -z "${bash_modules_path}" -o ! -d "${bash_modules_path}" ] && continue
	# check for sleep
	for bash_module_sleep in "sleep" "sleep.so"; do
	if [ -f "${bash_modules_path}/${bash_module_sleep}" ]; then
	if enable -f "${bash_modules_path}/${bash_module_sleep}" sleep 2>/dev/null; then
	mysleep="mysleep_builtin"
	# echo >&2 "$0: Using bash loadable ${bash_modules_path}/${bash_module_sleep} for sleep"
	break
	fi
	fi
	done
	[ ! -z "${mysleep}" ] && break
	done
	fi