startstop: Use the current directory as default TCOLLECTOR_PATH

With the current directory as default TCOLLECTOR_PATH the startstop
script can be called in the tcollector root without setting
TCOLLETOR_PATH.

Signed-off-by: Vasiliy Kiryanov <vasiliy.kiryanov@gmail.com>
use directory of the startstop script as default TCOLLECTOR_PATH

Signed-off-by: Vasiliy Kiryanov <vasiliy.kiryanov@gmail.com>
startstop: replace $BASH_SOURCE with a sh compatible variant

Signed-off-by: Vasiliy Kiryanov <vasiliy.kiryanov@gmail.com>