tests: use `assertAlmostEqual` for float comparison
Floating point arithmetics often lead to unsignificant differences between
expected and computed values (this is the typical example of 0.1 + 0.2 != 0.3). Because of this, some tests using assertEqual to compare two floats
were failing. The Python method
[assertAlmostEqual](https://docs.python.org/2.7/library/unittest.html#unittest
.TestCase.assertAlmostEqual) can prevent these issues by comparing values up to
the seventh decimal place. To find all occurences, two RegExp were ran on all
files of the tests/ folder: assertEquals?(\\(.+, [0-9]+\\.[0-9]+\\)) and
assertEquals?(\\([0-9]+\\.[0-9]+).
Goes in part with similar MR in slapos.toolbox.