IMPALA-3494: Set IMPALA_THRIFT_VERSION patch level to +7
IMPALA-3494: Set IMPALA_THRIFT_VERSION patch level to +7

This will bring in two changes in Thrift patch 7:

1. THRIFT-1248: fix TMemoryBuffer pointer arithmetic (fixed in Thrift 0.9.3)
2. Fix TMemoryBuffer overflow (THRIFT-3821, not fixed in 0.9.3)

Change-Id: I1e97b27d163627aa0f82ceff9e1d82400a4dac07
Reviewed-on: http://gerrit.cloudera.org:8080/3166
Reviewed-by: Huaisi Xu <30acdc0e0c70256bb93448da7fef766de715aea2@cloudera.com>
Tested-by: Internal Jenkins

michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala