Storing the distance matrix in the shared memory in conditioned GMFs calculations

[micheles]

This should save memory and improve speed in large calculations. For instance, for the Maule earthquake with 8,043 sites one gets

# before
| calc_175, maxmem=29.0 GB   | time_sec  | memory_mb | counts |
|----------------------------+-----------+-----------+--------|
| total get_mu_tau_phi       | 143.2221  | 1_006     | 3      |

# after
| calc_176, maxmem=4.5 GB    | time_sec  | memory_mb | counts |
|----------------------------+-----------+-----------+--------|
| total get_mu_tau_phi       | 133.9945  | 1_006     | 3      |

[raoanirudh]

Nice