fix(agent): fail on start error for test and fail modes

[powersj]

This aligns the behavior of the --test and --once modes to match that of the general telegraf operations. Currently, if there is a failure during a call to an input's start telegraf will stop. This is not the case for --test and --once modes. In these cases, the error will print out, but not stop execution. This can lead to crashes due to some variables not getting correctly initialized or setup in Start.

fixes: #12350

[telegraf-tiger[bot]]

Download PR build artifacts for linux_amd64.tar.gz, darwin_amd64.tar.gz, and windows_amd64.zip. Downloads for additional architectures and packages are available below.

:relaxed: This pull request doesn't significantly change the Telegraf binary size (less than 1%)

:package: Click here to get additional PR build artifacts

Artifact URLs

DEB	RPM	TAR GZ	ZIP
amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	darwin_arm64.tar.gz	windows_arm64.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz	windows_i386.zip
armhf.deb	i386.rpm	freebsd_armv7.tar.gz
i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
		linux_s390x.tar.gz
		static_linux_amd64.tar.gz