Add tests for get_bundles_from_transactions_hashes util method

[lzpap]

Solves: #302

Description

Source code changes:

• Raise a BadApiResponse exceptions when getTrytes returns empty trytes.

Test code changes:

• Add tests for get_bundles_from_transactions_hashes:
  • Single tx bundle successfully fetched given tail with inclusion states,
  • Single tx bundle successfully fetched given tail without inclusion states,
  • Called with empty list,
  • Exception is raised when node returns empty trytes,
  • Called with tail transactions, multiple bundles are fetched,
  • Called with a non-tail transaction, tail and bundle correctly fetched,
  • Returned bundles are sorted in ascending order based on timestamp.

[todofixthis]

LGTM