Stop using PYTEST_ADDOPTS in CircleCI to run xdist

xdist was not using the locally packaged trinity for tests,
so we had to disable it to correctly test packages.
But when xdist is removed, the -n parameter
that's in the environment causes pytest to fail.

Having a different environment on circle than local tests is likely to
cause future problems of a similar variety anyway, so let's just remove
the variable. This requires manually setting '-n 4' on the tests that
make sense with it, but making that value explicit seems like an
improvement.

pytest.ini

@@ -1,5 +1,5 @@
 [pytest]
-addopts= --showlocals
+addopts= --showlocals --durations 50 --maxfail 10
 python_paths= .
 xfail_strict=true
 log_format = %(levelname)8s  %(asctime)s  %(filename)20s  %(message)s

tox.ini

@@ -15,21 +15,20 @@ ignore=
 [testenv]
 usedevelop=True
 passenv =
-    PYTEST_ADDOPTS
     TRAVIS_EVENT_TYPE
 commands=
-    core: pytest {posargs:tests/core/}
-    eth2: pytest {posargs:tests/eth2}
-    p2p: pytest {posargs:tests/p2p}
-    rpc-blockchain: pytest {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'not GeneralStateTests'}
-    rpc-state-frontier: pytest {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and Frontier'}
-    rpc-state-homestead: pytest {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and Homestead'}
-    rpc-state-tangerine_whistle: pytest {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and EIP150'}
-    rpc-state-spurious_dragon: pytest {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and EIP158'}
+    core: pytest -n 4 {posargs:tests/core/}
+    eth2: pytest -n 4 {posargs:tests/eth2}
+    p2p: pytest -n 4 {posargs:tests/p2p}
+    rpc-blockchain: pytest -n 4 {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'not GeneralStateTests'}
+    rpc-state-frontier: pytest -n 4 {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and Frontier'}
+    rpc-state-homestead: pytest -n 4 {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and Homestead'}
+    rpc-state-tangerine_whistle: pytest -n 4 {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and EIP150'}
+    rpc-state-spurious_dragon: pytest -n 4 {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and EIP158'}
     # The following test seems to consume a lot of memory. Restricting to 3 processes reduces crashes
-    rpc-state-byzantium: pytest -n3 {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and Byzantium'}
-    rpc-state-constantinople: pytest -n3 {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and Constantinople'}
-    rpc-state-quadratic: pytest {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and stQuadraticComplexityTest'}
+    rpc-state-byzantium: pytest -n 3 {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and Byzantium'}
+    rpc-state-constantinople: pytest -n 3 {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and not stQuadraticComplexityTest and Constantinople'}
+    rpc-state-quadratic: pytest -n 4 {posargs:tests/json-fixtures-over-rpc/test_rpc_fixtures.py -k 'GeneralStateTests and stQuadraticComplexityTest'}
     lightchain_integration: pytest --integration {posargs:tests/integration/test_lightchain_integration.py}
 
 deps = .[p2p,trinity,test]
@@ -44,7 +43,6 @@ whitelist_externals=
     make
 deps = .[p2p, trinity, doc]
 passenv =
-    PYTEST_ADDOPTS
     TRAVIS_EVENT_TYPE
 commands=
     make validate-docs
@@ -82,7 +80,6 @@ use_develop=false
 [common-integration]
 deps = .[p2p,trinity,test]
 passenv =
-    PYTEST_ADDOPTS
     TRAVIS_EVENT_TYPE
 commands=
     pip install -e {toxinidir}/trinity-external-plugins/examples/peer_count_reporter