Use PrefixedWriter in logging commands in integration_test_runner.
Use PrefixedWriter in logging commands in integration_test_runner.

Signed-off-by: David Wadden <ff4ebafbe4a7d77cde45f9afefafd7a5dfa94f36@pivotal.io>

SrinivasChilveri/lattice,davidwadden/lattice-release,SrinivasChilveri/lattice,SrinivasChilveri/lattice,davidwadden/lattice,datachand/lattice,mikegehard/lattice,svrc-pivotal/lattice,Klaudit/lattice,davidwadden/lattice-release,svrc-pivotal/lattice,Klaudit/lattice,mikegehard/lattice,cloudfoundry-incubator/ltc,felipeg48/lattice,datachand/lattice,svrc-pivotal/lattice,davidwadden/lattice,svrc-pivotal/lattice,datachand/lattice,Klaudit/lattice,Klaudit/lattice,SrinivasChilveri/lattice,felipeg48/lattice,datachand/lattice,cloudfoundry-incubator/ltc