[disk] handle multilines df output

[degemer]

What does this PR do?

remove missing method _is_number in disk check.

Motivation

Fix #2732

Additional Notes

The previous method was:

try:
    float(my_var)
except:
    return False
return True

[degemer]

This is not the right way to do it. I'll update once we know more.

[degemer]

Updated with a test, it works now!

[olivielpeau]

Nitpick: the output seems to be aligned by column, it might be good to make sure the fixture has all the extra white spaces this implies (see

dd-agent/tests/test_system.py

Lines 39 to 51 in a681245

	linux_df_k = """Filesystem 1K-blocks Used Available Use% Mounted on
	/dev/sda1 8256952 5600592 2236932 72% /
	none 3802316 124 3802192 1% /dev
	none 3943856 0 3943856 0% /dev/shm
	none 3943856 148 3943708 1% /var/run
	none 3943856 0 3943856 0% /var/lock
	none 3943856 0 3943856 0% /lib/init/rw
	/dev/sdb 433455904 305360 411132240 1% /mnt
	/dev/sdf 52403200 40909112 11494088 79% /data
	nfs:/abc/def/ghi/jkl/mno/pqr
	52403200 40909112 11494088 79% /data
	/dev/sdg 52403200 40909112 11494088 79% /data
	"""

)

[degemer]

Nice 👀

[olivielpeau]

Added 2 nitpicks, but overall this looks 💚 !

Feel free to merge once they're addressed

[degemer]

Thanks for the review, I addressed both comments, waiting for 🍏 .

[olivielpeau]

💚 (CI failure is caused by an elasticsearch test that fails during setup, unrelated)